ABSTRACT To address the shortage of mental health specialists worldwide, with as few as 2 per 100,000 population in many low- and middle-income countries (LMICs), researchers and program implementers are using task sharing strategies, which involve delegating the provision of mental health care to a broader cadre of nonspecialists such as primary care physicians, community health workers, lay volunteers, and the service users themselves (i.e., peers). While evidence demonstrates that task sharing for mental health strategies is effective in improving detection and treatment for a range of mental disorders, there remains a lack of critical knowledge on how to successfully implement and scale up task-sharing strategies in real-world settings. To address this gap, the proposed study seeks to validate the Barriers and Facilitators in Implementation of Task Sharing in Mental Health (BeFITS-MH) measure, a multi-dimensional, multi-stakeholder tool we developed to enable the systematic and rapid assessment of core, modifiable barriers and facilitators factors. We developed BeFITS-MH using a multi-level conceptual model that we derived from influential implementation science frameworks, and analyzed qualitative data from three NIMH-funded global ?hubs? and a systematic review of barriers and facilitators identified in the literature. BeFITS-MH assesses perspectives from clients and providers, on 6 domains: 1) role fit; 2) satisfaction and motivation; 3) provider competence; 4) contextual congruence; 5) service accessibility; and 6) support systems. This study seeks to evaluate the psychometric and pragmatic properties of BeFITS-MH in 3 ongoing NIMH studies across 3 countries. Our Specific Aims are: Aim 1: Finalize the BeFITS-MH tool by finalizing the tool via a modified Delphi process and piloting the tool to evaluate the initial content validity and pragmatic qualities (i.e., time to complete). Aim 2: Evaluate the psychometric properties of BeFITS-MH tool. Following current Psychometric Evidence Scale criteria, we will evaluate internal consistency, norms, responsiveness, structural validity, convergent validity, discriminant validity, known-groups validity, and predictive validity. The tool will be validated against three implementation outcomes: acceptability, appropriateness, and feasibility, and process indicators at each site across two timepoints of data collection. Aim 3: Assess the pragmatic qualities and cross-national utility of BeFITS-MH. We will further understanding of implementation science and conceptual frameworks for TSMH strategies by exploring structural validity of the BeFITS-MH scales across sites. This research will contribute to NIMH Strategic Plan Objective 4: ?Strengthen the Public Health Impact of NIMH-Supported Research.? This study will also enable identification of core latent variables underlying modifiable barriers and facilitators across diverse contexts, thus advancing conceptualization of causal relationships among implementation outcomes. Findings will be useful within the U.S. and globally.